One of the small pleasures of life is to win a technical argument with a graduate student. You feel good, as well you should. It is only human to want to be right. Besides, if you ended up being wrong all or most of the time, you should start questioning your sanity: Why are they the students and you the supervisor, rather than the other way around? (One of the most hypocritical lies in the world is the cliché "I make sure to hire people who are smarter than I am." Sure. So obviously uttered—unless the person you are hiring is your successor — for the sole purpose of making you look whip-smart. If it were sincere, why then would you stay on?)
One of the big pleasures of life is to lose an argument with a graduate student. Then you have learned something.